Dividing Eq. 4.47 by gives an
expression relating the transmission coefficient to the
reflection coefficient

(4.53)

Although and depend on both
and , Snell's law (Eq. 4.46)
can be used to relate them to a single angle.

There are two characteristic angles associated with a planar
interface, Brewster's angle, the angle at which no reflection
occurs, and the critical angle, the angle above
which total internal reflection occurs. You will consider these for
homework.

For normal incidence,
, and the incident, reflected, and transmitted waves lie along a
single axis. Eq.'s 4.52 and 4.53 become

(4.54)

and

(4.55)

Caution! The reflection and transmission coefficients
and above describe amplitudes, not intensities. You will
use these coefficients to derive similar coefficients for intensity
for homework.